As computers and other electronic devices become more popular, touch-sensing systems are becoming more prevalent as a means for inputting data. For example, touch-sensing systems can be found in automatic teller machines, personal digital assistants, casino game machines, mobile phones, and numerous other applications.
Capacitive touch sensing is one of the most widely used techniques in touch screen industries. Capacitive touch sensors are mainly divided in two groups, namely, continuous capacitive sensors and discontinuous (patterned) capacitive sensors. In a continuous capacitive sensor, the sensor includes a sheet of conducting thin film that is electrically excited from four corners of the touch screen. The signals induced by a user's touch are transmitted from the four corners to a controller, where they are decoded and translated into coordinates. In a typical patterned capacitive touch screen, the sensor may include one or more series of parallel conductive bars that are driven from one or both ends with excitation signals from a controller coupled to the conductive bars by lead lines. The signals induced by a user's touch may be transmitted to the controller with the same lead lines that excite the sensor bars. These signals may then be decoded in the controller and the touch coordinates may be reported to a computer.
Touch sensors utilizing more than one patterned sensing layer are often used to determine the coordinates of a touch with high accuracy, provided that the sensing layers have a suitable pattern geometry. One example of a touch screen assembly 10 that includes two patterned conductive layers 12 and 14 is shown in FIG. 1A and FIG. 1B. The patterned conductive layers 12 and 14 may be made from a transparent conductive material, such as indium tin oxide (ITO), and each layer is generally disposed on a transparent substrate (not shown here). Each row of conductive elements of each of the sensor layers 12 and 14 includes a series of diamond-shaped electrodes that are connected to each other with short strips of relatively narrow rectangles. A dielectric layer 16 separates the two conductive layers 12 and 14, and serves to prevent them from coming into direct contact with each other. As an example the dielectric layer 16 may include an adhesive manufactured from any non-conductive, transparent material.
As shown, the end of each row of the two patterned conductive layers 12 and 14 is coupled to one of a set of traces 18 (e.g., silver traces) that are in turn coupled to a controller 20. Generally, the traces 18 are used to couple the electrodes to the controller 20 because the resistance of the ITO conductive layer is relatively high. The resistance of the ITO conductive layer is relatively high because the amount of conductive material used in the ITO compound is kept relatively low so that the layer is substantially transparent. The traces 18 may generally be deposited on to the substrate using any suitable process. One method includes vacuum sputtering a metal layer (e.g., aluminum or Mo—Al—Mo) onto the substrate, then etching the traces 18 using a photo etching process. Another method includes silk-screen printing silver conductive ink to form the traces 18.
The controller 20 may include circuitry for providing excitation currents to the capacitive sensors 12 and 14 and for detecting signals generated by the sensors. Further, the controller 20 may include logic for processing the signals and conveying touch information to another part of an electronic device, such as a processor.
FIG. 2 illustrates the various layers that may be included in a touch screen sensor assembly 40. The assembly 40 includes a top substrate 42a and a bottom substrate 42b that are each coated with patterned ITO layers 44a and 44b, respectively, that include a plurality of electrodes. The substrates 42a and 42b may be configured from any suitable transparent material, including glass, plastic (e.g., PET), or the like. Further, the top ITO layer 44a may be separated from the bottom ITO layer 44b by a suitable dielectric spacer 48 that is adhered by optically clear adhesive layers 46a and 46b. 
As discussed above, the ITO layers 44a and 44b may be coupled to one or more controllers that are operable to excite and sense electrical signals on the electrodes of the ITO layers 44a and 44b. To electrically connect the controller to the ITO layers 44a and 44b, a flexible printed circuit (FPC) 56 may be coupled to the assembly 40. The FPC 56 may include an FPC substrate 55, top copper traces 54a, and bottom copper traces 54b that are used to couple the top and bottom ITO layers 44a and 44b to a controller. To make the connection between the copper traces 54a and 54b and the ITO layers 44a and 44b, traces 50a and 50b may be disposed in contact with portions of the ITO layers. Further, the traces 50a and 50b may be coupled to the copper traces 54a and 54b using electrically conducive adhesive layers 52a and 52b, which may, for example, include an anisotropic conductive adhesive (ACA).